Case history: A 5 km long waterborne geophysical survey along the Po river within the city of Turin (northwest Italy)

The geologic investigation of water-covered areas is often difficult and inefficient with only the use of traditional surveying techniques (i.e., local drilling and sampling). Waterborne geophysical surveys can offer a valuable alternative to achieve adequate data coverage in a cost-effective way. Two geophysical waterborne methods were combined in this study for the delineation of the submerged subsurface geology along a 5 km stretch of the Po river, within the urban area of Turin. The adopted methods were: continuous vertical electrical sounding (CVES) and ground-penetrating radar (GPR). Special attention was devoted to the accurate geo-referencing of both surveys for combined interpretation. GPR results provide a high-quality representation of the river bed forms, with identification of clear sand dunes in the finer alluvial sediments. CVES resistivity sections enable a deeper characterization, identifying the interface between the shallow alluvial deposits and the deeper low-resistivity marls of the Turin-Hill succession. Our work strengthens the effectiveness of waterborne surveys for geologic prospecting of water-covered and difficult-to-access areas.